This specification relates to coupling light using a grating.
Light propagates inside a photonic integrated circuit, and is coupled to an external medium through a grating fabricated on the photonic integrated circuit. Conventionally, coupling between light and the photonic integrated circuit is achieved by an edge coupling, where an optical facet needs to be prepared and the process is time-consuming and expensive. An emission of a laser diode in the photonic integrated circuit is coupled to the external medium through a grating. Two terminals of the laser diode are used to inject electrical carriers to generate photons, and the photons resonate in a cavity and emit coherent light.